Presently, biological pest control methods have become popular increasingly. With regard to biological control, the population quantity of pests is controlled with metabolic products of various beneficial animals or organisms in the natural world, so as to ultimately protect normal growth of crops. Among existing biological control methods, the methods of insect pest control are widely applied. There are many kinds of animals that prey on pests, such as ladybugs, lacewings, wasps, hoverflies, and spiders, etc. Those natural enemies of pests have a big appetite and can attain a good pest control effect. Parasitic natural enemies mainly include parasitic wasps and parasitic flies, such as trichogramma, which lay eggs inside larvae or kidneys of pests, and thereby inhibit pest propagation. Insect pest control is applied most widely, and is a main content of biological control.
For biological control of diseases and pests, releasing natural enemies is a main technical problem. In the prior art, natural enemies are mainly released with a manual releasing method, which has low releasing efficiency and is unsuitable for large-area operation.
In view of that problem, automatic distributing devices have been conceived, to distribute natural enemies with assistance of an airplane, for example in the Patent Application with application No. 201120328245.9 and entitled “Natural Enemy Distributor for Airplane”, during use, natural enemies are loaded into a box, the motor speed is adjusted to control the rotation of impellers, and thereby the natural enemies are transferred to a conveyer belt at a constant speed, conveyed by the conveyer belt, distributed into a natural enemy spray duct, and then distributed onto a motor-driving rotating disc through the natural enemy spray duct, and thrown away under centrifugal force; thus, the distributing efficiency is effectively improved while the natural enemies are distributed in a large area. However, the device has low reliability and is difficult to be installed on an airplane; the survival ratio of the natural enemies is low owing to the fact that the natural enemies may contact with the rotating blades rigidly; the quantity of natural enemies distributed in some areas may be too high or too low, because the device cannot distribute at intervals.
For example, a natural enemy distributing device is disclosed in Patent Application No.201220699049.7 entitled “Natural Enemy Distributing Device for Airplane”, wherein, the natural enemies are distributed by means of a motor-driving support frame under centrifugal force. However, the device can't control the distributing time accurately; in addition, the device cannot control the distributing quantity of natural enemies accurately and has low reliability, owing to size differences of the natural enemies.
All of the above-mentioned patents utilize the centrifugal force to distribute natural enemies, have many defects and low reliability, and the centrifugal force may have impact on the flight stability of the airplane.